Thermally assisted magnetic recording (TAMR) is expected to be one of the future generation magnetic recording technologies that will enable recording at 1˜10 Tb/inch2 data density. TAMR converts optical power into localized heating of the magnetic recording medium to temporarily reduce the field needed to switch the magnetizations of the medium grains. With a sharp temperature gradient alone, or together with the magnetic field gradient when both gradients are aligned correctly, data storage density can be further improved over the current state-of-the-art magnetic recording technology.
A TAMR head usually comprises, in addition to its conventional magnetic recording structure, an optical wave-guide (WG) and a Plasmon generator (PG). The WG serves to guide external laser light to the PG, where the optical mode is coupled to the Plasmon mode of the PG. After being converted to plasmon mode the optical energy then concentrated at the location where heating of the medium is required. When the heating spot is correctly aligned relative to the write field of the magnetic recording structure, TAMR is achieved.
We refer now to the prior art air bearing surface (ABS) view shown in FIG. 1a. This illustrates a TAMR head located at the end of main pole 10, integrated with Edge Plasmon generator (EPG) 15 and having, in cross-section, triangular shape 16. This shaped edge is placed in the vicinity of optical waveguide 11 where it supports the very confined Edge Plasmon (EP) mode. The optical energy in WG 11 is efficiently transformed to edge plasmon mode through evanescent coupling and its energy is directed towards the ABS. The local confinement of the edge plasmon mode is determined by the angle and radius of 16's triangular corner, by the noble metal from which the EPG is formed, as well as by the dielectric material that surrounds tip 16.
Referring next to FIG. 1b, for a 25 nm tip radius, the size of optical spot 18 in recording medium 9 is about 100 nm across its half-maximum intensity area. By placing plasmon shield 12 a small dielectric gap distance from EPG 15, optical spot 18 can be further reduced in size since, in the presence of plasmon shield 12, the spot size is mainly determined by PSG which is gap distance 13 between edge plasmon generator 15 and plasmon shield 12. For example, a 50 nm optical spot size can be achieved if this gap distance is less than 40 nm.
Plasmon shield 12 is placed at the front of wave-guide 11. Using the current (prior art) process, the top surface of plasmon shield 12 is at the same level as the top surface of WG 11 or even slightly lower than the top surface of WG 11 due to different CMP rates for the Au of layer 15 and the Ta2O5 used for WG 11.
When PSG 13 is scaled down, WEG 19 (the gap between WG 11 and EPG 15) will also be reduced. One consequence of a reduced WEG is poorer optical coupling efficiency between WG 11 and EPG 15, so some optical power will be wasted as a result. This coupling efficiency cannot be improved by fine turning the length of EPG 15 when WEG 19 is less than 25 nm. Thus, to simultaneously achieve both good optical efficiency and a small optical spot, it is important to have both a large fixed WEG as well as a small PSG.